Add caching to trace file loaders
Add caching to trace file loaders

We know the file contents don't change, so let's only load each file
once and cache it in memory after that :)

Bug: 1386092
Change-Id: Ie8fbc8812a6bd5a4bf9a04680f4499783b9abc7e
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/4055601
Commit-Queue: Nancy Li <75d1eae50692fe1e75f263dbfd52feffc9e7984f@chromium.org>
Commit-Queue: Jack Franklin <993fcadce4d04090da2fefd557a0995e7966c8d5@chromium.org>
Auto-Submit: Jack Franklin <993fcadce4d04090da2fefd557a0995e7966c8d5@chromium.org>
Reviewed-by: Nancy Li <75d1eae50692fe1e75f263dbfd52feffc9e7984f@chromium.org>

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